Heteroleptic Iridium(III) Complexes with Phenylpridine and Diphenylquinoline Derivative Ligands

Abstract

The synthesis and photophysical study of efficient phosphorescent iridium(III) complexes having two different (C ˆ N) ligands are reported. In order to improve the luminescence efficiency by avoiding triplet-triplet (T-T) annihilation, the iridium complexes, Ir(ppy)2(dpq) and Ir(ppy)2(dpq-3-F), are designed and prepared where ppy, dpq and dpq-3-F represent 2-phenylpyridine, 2,4-diphenylquinoline and 2-(3-fluorophenyl)-4-phenylquinoline, respectively. Since Ir(ppy)3, Ir(dpq)3 and Ir(dpq-3-F)3 can be placed in the metal-to-ligand charge transfer (MLCT) excited state, they absorb light effectively. Thus, ppy ligands and a dpq derivative can act as a source of energy supply. When Ir(ppy)2(dpq-3-F) is placed in the lowest excited state, the excitation energy is not quenched nor deactivated but quickly transferred intramolecularly from two ppy ligands to one luminescent dpq-3-F ligand. Such transfer can occur because the triplet energy level of ppy is higher than that of dpq-3-F and light is emitted from dpq-3-F ligand in the end. Thus, Ir(ppy)2(dpq-3-F) shows strong photoluminescence from dpq-3-F ligand. To analyze luminescent mechanism, we calculated these complexes theoretically by using computational method.